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  1. 23 9月, 2012 5 次提交
    • P
      rcu: Avoid rcu_print_detail_task_stall_rnp() segfault · 5fd4dc06
      由 Paul E. McKenney 提交于 
      The rcu_print_detail_task_stall_rnp() function invokes
rcu_preempt_blocked_readers_cgp() to verify that there are some preempted
RCU readers blocking the current grace period outside of the protection
of the rcu_node structure's ->lock.  This means that the last blocked
reader might exit its RCU read-side critical section and remove itself
from the ->blkd_tasks list before the ->lock is acquired, resulting in
a segmentation fault when the subsequent code attempts to dereference
the now-NULL gp_tasks pointer.

This commit therefore moves the test under the lock.  This will not
have measurable effect on lock contention because this code is invoked
only when printing RCU CPU stall warnings, in other words, in the common
case, never.
Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
      5fd4dc06
    • P
      rcu: Apply for_each_rcu_flavor() to increment_cpu_stall_ticks() · 115f7a7c
      由 Paul E. McKenney 提交于 
      The increment_cpu_stall_ticks() function listed each RCU flavor
explicitly, with an ifdef to handle preemptible RCU.  This commit
therefore applies for_each_rcu_flavor() to save a line of code.

Because this commit switches from a code-based enumeration of the
flavors of RCU to an rcu_state-list-based enumeration, it is no longer
possible to apply __get_cpu_var() to the per-CPU rcu_data structures.
We instead use __this_cpu_var() on the rcu_state structure's ->rda field
that references the corresponding rcu_data structures.
Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
      115f7a7c
    • P
      rcu: Fix obsolete rcu_initiate_boost() header comment · b065a853
      由 Paul E. McKenney 提交于 
      Commit 1217ed1b (rcu: permit rcu_read_unlock() to be called while holding
runqueue locks) made rcu_initiate_boost() restore irq state when releasing
the rcu_node structure's ->lock, but failed to update the header comment
accordingly.  This commit therefore brings the header comment up to date.
Signed-off-by: NPaul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: NJosh Triplett <josh@joshtriplett.org>
      b065a853
    • P
      rcu: Improve boost selection when moving tasks to root rcu_node · 5cc900cf
      由 Paul E. McKenney 提交于 
      The rcu_preempt_offline_tasks() moves all tasks queued on a given leaf
rcu_node structure to the root rcu_node, which is done when the last CPU
corresponding the the leaf rcu_node structure goes offline.  Now that
RCU-preempt's synchronize_rcu_expedited() implementation blocks CPU-hotplug
operations during the initialization of each rcu_node structure's
->boost_tasks pointer, rcu_preempt_offline_tasks() can do a better job
of setting the root rcu_node's ->boost_tasks pointer.

The key point is that rcu_preempt_offline_tasks() runs as part of the
CPU-hotplug process, so that a concurrent synchronize_rcu_expedited()
is guaranteed to either have not started on the one hand (in which case
there is no boosting on behalf of the expedited grace period) or to be
completely initialized on the other (in which case, in the absence of
other priority boosting, all ->boost_tasks pointers will be initialized).
Therefore, if rcu_preempt_offline_tasks() finds that the ->boost_tasks
pointer is equal to the ->exp_tasks pointer, it can be sure that it is
correctly placed.

In the case where there was boosting ongoing at the time that the
synchronize_rcu_expedited() function started, different nodes might start
boosting the tasks blocking the expedited grace period at different times.
In this mixed case, the root node will either be boosting tasks for
the expedited grace period already, or it will start as soon as it gets
done boosting for the normal grace period -- but in this latter case,
the root node's tasks needed to be boosted in any case.

This commit therefore adds a check of the ->boost_tasks pointer against
the ->exp_tasks pointer to the list that prevents updating ->boost_tasks.
Signed-off-by: NPaul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: NJosh Triplett <josh@joshtriplett.org>
      5cc900cf
    • P
      rcu: Properly initialize ->boost_tasks on CPU offline · 1e3fd2b3
      由 Paul E. McKenney 提交于 
      When rcu_preempt_offline_tasks() clears tasks from a leaf rcu_node
structure, it does not NULL out the structure's ->boost_tasks field.
This commit therefore fixes this issue.
Signed-off-by: NPaul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: NJosh Triplett <josh@joshtriplett.org>
      1e3fd2b3
  3. 06 7月, 2012 1 次提交
  5. 03 7月, 2012 11 次提交
  7. 07 6月, 2012 3 次提交
  9. 10 5月, 2012 2 次提交
    • P
      rcu: Explicitly initialize RCU_FAST_NO_HZ per-CPU variables · 98248a0e
      由 Paul E. McKenney 提交于 
      The current initialization of the RCU_FAST_NO_HZ per-CPU variables makes
needless and fragile assumptions about the initial value of things like
the jiffies counter.  This commit therefore explicitly initializes all of
them that are better started with a non-zero value.  It also adds some
comments describing the per-CPU state variables.
Signed-off-by: NPaul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
      98248a0e
    • P
      rcu: Make RCU_FAST_NO_HZ handle timer migration · 21e52e15
      由 Paul E. McKenney 提交于 
      The current RCU_FAST_NO_HZ assumes that timers do not migrate unless a
CPU goes offline, in which case it assumes that the CPU will have to come
out of dyntick-idle mode (cancelling the timer) in order to go offline.
This is important because when RCU_FAST_NO_HZ permits a CPU to enter
dyntick-idle mode despite having RCU callbacks pending, it posts a timer
on that CPU to force a wakeup on that CPU.  This wakeup ensures that the
CPU will eventually handle the end of the grace period, including invoking
its RCU callbacks.

However, Pascal Chapperon's test setup shows that the timer handler
rcu_idle_gp_timer_func() really does get invoked in some cases.  This is
problematic because this can cause the CPU that entered dyntick-idle
mode despite still having RCU callbacks pending to remain in
dyntick-idle mode indefinitely, which means that its RCU callbacks might
never be invoked.  This situation can result in grace-period delays or
even system hangs, which matches Pascal's observations of slow boot-up
and shutdown (https://lkml.org/lkml/2012/4/5/142).  See also the bugzilla:

	https://bugzilla.redhat.com/show_bug.cgi?id=806548

This commit therefore causes the "should never be invoked" timer handler
rcu_idle_gp_timer_func() to use smp_call_function_single() to wake up
the CPU for which the timer was intended, allowing that CPU to invoke
its RCU callbacks in a timely manner.
Reported-by: NPascal Chapperon <pascal.chapperon@wanadoo.fr>
Signed-off-by: NPaul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
      21e52e15
  11. 03 5月, 2012 2 次提交
  13. 01 5月, 2012 1 次提交
  15. 26 4月, 2012 1 次提交
    • P
      rcu: Add warning for RCU_FAST_NO_HZ timer firing · 79b9a75f
      由 Paul E. McKenney 提交于 
      RCU_FAST_NO_HZ uses a timer to limit the time that a CPU with callbacks
can remain in dyntick-idle mode.  This timer is cancelled when the CPU
exits idle, and therefore should never fire.  However, if the timer
were migrated to some other CPU for whatever reason (1) the timer could
actually fire and (2) firing on some other CPU would fail to wake up the
CPU with callbacks, possibly resulting in sluggishness or a system hang.

This commit therfore adds a WARN_ON_ONCE() to the timer handler in order
to detect this condition.
Signed-off-by: NPaul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
      79b9a75f
  17. 25 4月, 2012 3 次提交
  19. 22 2月, 2012 11 次提交